Single piece fuselage barrel

ABSTRACT

In accordance with the present invention an aircraft stringerless fuselage structure is provided comprising an impact compliant outer skin having a plurality of resin impregnated skin fibers forming an outer skin surface, an inner stringerless skin surface, and a skin thickness. A plurality of stiffeners is included, each comprising a plurality of resin impregnated stiffener fibers integrated into the inner stringerless skin structure. The plurality of resin impregnated skin fibers are not aligned with the plurality of resin impregnated stiffener fibers.

TECHNICAL FIELD

The present invention relates generally to an apparatus and method forreducing the cost and complexity of the fuselage barrel section of anaircraft and more particularly to an apparatus and method forintegrating a cost effective and compliant structure that absorbs energyduring bird strike impact.

BACKGROUND OF THE INVENTION

Aircraft structures often provide complex and costly challenges to bothdesign and manufacturing. The underlying structures must not only meetstrength requirements, but must also survive constant weight reductionrequirements and manufacturing cost and time restraints. As such, areanalysis and creative investigation into existing structures bears thepossible reward of considerable benefits during implementation.

Such is the case with the fuselage section of the aircraft. Specificallythe forward section commonly referred to as section 41. This fuselagesection includes complex geometry and structure by way of the inclusionof both the nose section as well as the cockpit windows and similarfeatures. Additionally, this portion of the aircraft comes under closescrutiny for its ability to have bird strike resistance. As such,section 41 barrel sections are often over designed which may lead toexcess weight and more commonly excess cost.

Present fuselage sections are commonly are centered around designs thatare stout and heavy. Often the outer skin and other structural supportsare formed from aluminum which when overloaded may result in costlydamage or repair. Bird strike incidents, even on designs that are notoverloaded, may leave large dents in the aluminum structure thateventually require costly repairs. When overloaded, however, portions ofthe aluminum structure may rupture requiring extremely expensive repairor replacement. The aluminum skin also requires complex manufacturingand assembly as the skin is commonly backed by very heavy and complexbeam structures. Structures such as stringers are required for supportand add both considerable cost in addition to weight to the aircraft.The complex curvatures of the skins, especially in the nose region,often require manufacturing using expensive computer controlledmachines. The quantity and complexity of manufacturing and assemblingthese aluminum structures often make section 41 the most expensivebarrel section in the entire aircraft body.

What is needed is a design and method for manufacturing this complexsection of the fuselage that allowed for simplification of manufacturingwhile simultaneously allowing for a compliant approach to bird strikeresistance. Additionally, it would be highly desirable to have such adesign and method that provided opportunities to reduce section weightin addition to manufacturing costs.

SUMMARY OF THE INVENTION

In accordance with the present invention an aircraft stringerlessfuselage structure is provided comprising an impact compliant outer skinhaving a plurality of resin impregnated skin fibers forming an outerskin surface, an inner stringerless skin surface, and a skin thickness.A plurality of stiffeners is included, each comprising a plurality ofresin impregnated stiffener fibers integrated into the innerstringerless skin structure. The plurality of resin-impregnated skinfibers are not aligned with the plurality of resin impregnated stiffenerfibers.

Other objects and features of the present invention will become apparentwhen viewed in light of the detailed description and preferredembodiment when taken in conjunction with the attached drawings andclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of an aircraft stringerless fuselage sectionin accordance with the present invention.

FIG. 2 is a detailed illustration of the impact compliant outer skinutilized in the fuselage section illustrated in FIG. 1.

FIG. 3 is a detailed cross-sectional illustration of a portion of theaircraft fuselage section illustrated in FIGS. 1 and 2. and

FIG. 4 is an illustration of a lay-up tool for use in the manufacturingof the aircraft fuselage section illustrated in FIGS. 1 and 2.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to FIG. 1, which is an illustration of an aircraftstringerless fuselage section 10 in accordance with the presentinvention. The section 10 is illustrated as the commonly known sectionforty-one section although it is contemplated that the present inventionis applicable to a variety of aircraft build zones. The section 10presented includes the nose portion 12 in addition to the cockpitwindows 14 wherein the geometry of the barrel section 10 is variedconsiderably in addition to requiring additional strength requirements.One of these requirements is the ability to withstand bird impact loadsduring operation. Existing designs contemplate the use of aluminum skinsand complex and costly support structures underneath such as the use ofcomplex curved stringers or other beams. In addition, existingapproaches often result in costly repairs during bird strike due totheir rigid approach to bird strike protection.

The present invention accomplishes both weight savings and bird strikeprotection through a unique combination of the use of a uniquely birdstrike compliant outer skin 16 (impact resistant) that allows aredirection of bird path without damage in combination with theintegration therein of a plurality of stiffeners 18, preferablycircumferentially orientated, that provide sufficient structural supportof the skin 16 without debonding during bird strike and withoutdiminishing the skin compliance. It should be understood that inaddition to pure circumferential orientation, perpendicular to the axis,variations of angled circumferential orientation, including intersectingstiffeners angled relative to the axis, are contemplated. The presentinvention contemplates the use of an impact resistant outer skin 16 thatis tailored to be compliant and absorb or redirect the impact of birdstrikes. The present invention accomplishes this through the use of askin 16 formed from a plurality of resin impregnated skin fibers 20forming a skin 16 having an outer skin surface 22, an inner stringerlessskins surface 24, and a skin thickness 26. It is contemplated that theplurality of impregnated skin fibers 20 is intended to include bothpre-preg tape or dry fibers with infused resin.

A key characteristic, however, is that the skin thickness 26 iscontemplated to be variable to accommodate the strength requirements ofdiffering bird impact zones or structural zones (such as the cockpitwindows 14) of the barrel section 10. It is contemplated that skinthickness 26 be variable between the range of 0.08 inches and 0.25inches to provide the proper strength to weight ration. It iscontemplated that the skin 16 be formed using high strain fibers such asspectra, vectran, low modulus GR, or even fiberglass. These fibers arechosen to provide a compliant structure that instead of crushing orrupturing during impact, instead deforms and deflect the birdtrajectory. Additional contemplated feature include the use of hybridlaminates wherein two or more fiber types are utilized in order toachieve the desired strength/compliance characteristics. One specificembodiment contemplates that the skin 16 be formed using an intermediatemodulus (22-25 MSI) toughened carbon pre-preg tape. It is furthercontemplated that the use of 0/45/90 degree laminate mixture at 20/80/0percentage ratios provides the preferably structural characteristics forthe skin 16. The present invention contemplates the use ofnon-traditional fiber angles in laminates to achieve the desiredstrength/conformity properties.

By designing an impact conforming (resistant) outer skin 16 with uniqueconstruction and properties, the present invention paves the way forelimination of the need for stringers in the barrel section 10. Thissaves weight in addition to manufacturing costs. The present invention,instead, relies on the use of low profile and low modulus stiffenerelements such as the hat frame assembly 28 illustrated in FIG. 3 for useas the circumferentially orientated stiffeners 18. Although hat framesare specifically described and illustrated, it is contemplated that thestiffener elements 28 may include, but are not limited to, hat frames,c-channels, Z-beams, J-beams, T-Beams and I-beams, and blade stiffenedbeams. The hat frames 28 are preferably formed to comply with toughenedouter skin 16 and are formed using a plurality of resin impregnatedstiffener fibers 30 (preferably low-modulus fibers). These low modulusstiffener fibers 30 are preferably fully integrated into the skin fibers20 of the inner stringerless skin surface 24 and co-cured to form asingle element. The low modulus stiffener fibers 30 are preferably highstrain fibers such as fiberglass, spectra, vectran, or low modulus GR.Similar to the skin 16 it is contemplated that hybrid laminates andnon-traditional lay-up angles may be utilized to achieve the desiredconformity during impact while retaining sufficient structural support.In one embodiment, the low modulus frame stiffener fibers 30 arepreferably layed up as +/−60 degree laminates. Although a variety oflay-up arrangements may be utilized, it is preferably that the stiffenerfibers 30 are not aligned (0 or 90 degrees) with the skin fibers 20. Thehat frame assembly 28 preferably is designed with both a low profile anda low modulus to resist debonding with the outer skin 16 during birdimpact. It is contemplated that low profile is intended to comprise aprofile height 31 of less than 3 inches and preferably less than 2inches. It is further contemplated that low modulus is intended tocomprise approximately 3-25 MSI. One embodiment contemplates the use ofcarbon fiber impregnated with epoxy for use in forming the hat frameassembly 28.

In one embodiment of the hat frame assembly 28, the assembly includes afirst frame foot 32 and a second frame foot 34. A first angled sidewall36 and second angled sidewall 38 proceed out of their respective feetand extend toward a hat top portion 40 joining the sidewalls 36,38. Thishat frame assembly 28 thereby defines a hat frame interior 42 which islocated between the hat top 40 and the outer skin 16 when the feet 32,34 are bonded to the inner stringerless skin surface 34. Although avariety of hat frames 28 are contemplated, one embodiment contemplates aframe wall thickness 44 of approximately 0.05 inches. This, incombination with the low profile helps provide the low moduluscharacteristics suitable for impact protection and stringerless support.

The hat frame assembly 28 can further include one or more cap elements46 integrated into the hat top portion 40 of the hat frame assembly 28.As is illustrated, one embodiment contemplates the use of a pair ofvertically stacked cap elements. The cap elements 46 are preferably lowdensity caps such as fiberglass caps or preferably S-2 glass plies. Inone embodiment it is contemplated that the cap comprise a cap width 48between the range of 0.08 inches and 0.15 inches. It is desirable thatthe cap elements 46 be comprised of 0 degree laminates interleaved withthe resin impregnated stiffener fibers 30. The hat frame assembly 28 mayalso include a pcf foam element 50 (3-7 pcf) that also may be tailoredto individual impact zones or skin thicknesses 26. The use of the foamelement 50 allows for a further tailoring of impact resistance withoutnegatively impacting either weight or the low modulus nature of the hatassembly 28 and skin 16 interaction that provides compliance andprevents damage or debonding during impact while continuing to provideenough structural rigidity to allow for the elimination of stringers.

The present invention, in addition to providing a vastly improvedstructure and approach to bird strike damage reduction, also provides avastly improved methodology of manufacturing and assembling the aircraftfuselage section. Prior approaches required the use of aluminum skinwith complex multi-curved shapes and corresponding beam stringers withmatching curves. The present invention, however, yields a far more costeffective and efficient method of manufacturing and assembly. Thepresent invention contemplates the use of a fuselage lay-up tool 52incorporating a plurality of multi-curved shapes 54 along its length.The lay-up tool 52 includes a plurality of stiffener grooves 56 on itsupper tool surface 58. The stiffener grooves 56 are configured to allowthe low modulus stiffener fibers 30 to be laid up directly onto thegrooves 56 and thereby form a hat frame assembly 28 or other stiffenerconfiguration. The stiffener grooves 56 further allow the stiffeners 28to be located precisely in relation to both each other and the overallfuselage section 10. The skin fibers 20 may then be laid-up over the lowmodulus stiffener fibers 30 to complete the integrated skin/frameassembly and then the whole assembly may be cured as a single entity.This contemplates co-curing where the stiffener fibers 30 are laid ingreen, the skin fibers 20 are applied on top, and the whole assembly issimultaneously cured. This further contemplates co-bonding wherein thestiffener fibers 30 are cured prior to the application of the skinfibers 20. This allows the fuselage to be created as a single entitywith double curved or multi-curved characteristics. Thereby complex skinshapes are accommodated in addition to the bonding of complex framesconcurrently. This has the potential for generating both savings as wellas performance improvements to fuselage design and production.

While the invention has been described in connection with one or moreembodiments, it is to be understood that the specific mechanisms andtechniques which have been described are merely illustrative of theprinciples of the invention, numerous modifications may be made to themethods and apparatus described without departing from the spirit andscope of the invention as defined by the appended claims.

1. An aircraft stringerless fuselage structure comprising: an impactcompliant outer skin comprising a plurality of resin impregnated skinfibers forming an outer skin surface, an inner stringerless skinsurface, and a skin thickness; and a plurality of stiffeners eachcomprising a plurality of resin impregnated stiffener fibers, each ofsaid stiffeners integrated into said inner stringerless skin structure;wherein said plurality of resin impregnated skin fibers are not alignedwith said plurality of resin impregnated stiffener fibers, saidstructure being adapted to absorb or redirect the impact of birdstrikes.
 2. An aircraft stringerless fuselage structure as described inclaim 1, further comprising: a plurality of axially orientated hat frameassemblies wherein each of said axially orientated hat frame assembliescomprises both low profile and low modulus stiffeners.
 3. An aircraftstringerless fuselage structure as described in claim 1, wherein each ofsaid stiffeners comprises: a hat frame assembly comprising: a firstframe foot; a second frame foot; a first angled frame sidewall extendingfrom said first frame foot; a second angled frame sidewall extendingfrom said second frame foot; and a hat top connecting said first angledframe sidewall to said second angled frame sidewall, said hat frameassembly defining a hat frame interior.
 4. An aircraft stringerlessfuselage structure as described in claim 3, further comprising: at leastone cap element positioned within said hat top.
 5. An aircraftstringerless fuselage structure as described in claim 3, furthercomprising a pcf foam element filling said hat frame interior.
 6. Anaircraft stringerless fuselage structure as described in claim 4,wherein: said impact compliant outer skin being formed using a laminatemixture of 0/45/90 degree layup at 20/80/0 percentage ratios; each ofsaid axially oriented frames comprises +/−60 degree layup; and said atleast one cap element comprises 0 degree layup interweaved with saidresin impregnated frame fibers.
 7. An aircraft stringerless fuselagestructure as described in claim 4, wherein said at least one cap elementcomprises a pair of vertically stacked cap elements.
 8. An aircraftstringerless fuselage structure as described in claim 1, wherein: saidskin thickness is varied between 0.25 inches and 0.08 inches to bespecifically tailored to bird impact requirements; and said stiffenerscomprise a frame wall thickness of 0.05 inches.
 9. An aircraftstringerless fuselage structure as described in claim 4, wherein each ofsaid cap elements comprises a cap width of 0.08 to 1.5 inches.
 10. Anaircraft stringerless fuselage structure comprising: an impact compliantouter skin comprising an outer skin surface, an inner stringerless skinsurface, and a skin thickness, said impact compliant outer skincomprising a plurality of resin impregnated skin fibers; and a pluralityof circumferentially orientated hat frames, each of saidcircumferentially orientated frames integrated into said innerstringerless skin surface.
 11. An aircraft stringerless fuselagestructure as described in claim 10, wherein: said plurality ofcircumferentially orientated hat frames comprises a plurality of resinimpregnated stiffener fibers, said plurality of resin impregnated skinfibers are not aligned with said plurality of resin impregnatedstiffener fibers.
 12. An aircraft stringerless fuselage structure asdescribed in claim 10, wherein each of said circumferentially orientatedhat frames comprises: at least one low density cap element positioned ina hat top of said axially orientated hat frame.
 13. An aircraftstringerless fuselage structure as described in claim 10, wherein saidplurality of resin impregnated skin fibers comprise high strain fibers.14. An aircraft stringerless fuselage structure as described in claim11, wherein said resin impregnated stiffener fibers are co-cured to saidresin impregnated skin fibers.
 15. An aircraft stringerless fuselagestructure as described in claim 10, wherein said impact compliant outerskin comprises a hybrid laminate tailored to provide bird strike impactcompliance.
 16. An aircraft stringerless fuselage structure as describedin claim 15, wherein said hybrid laminate comprises a plurality ofvaried lay-up angles tailored to provide bird strike impact compliance.17. An aircraft stringerless fuselage structure as described in claim10, wherein said plurality of circumferentially orientated hat framescomprise low modulus hat frames configured to resist debonding from saidimpact compliant outer skin during bird impact.
 18. A method of formingan aircraft fuselage structure void of stringers comprising: utilizing afuselage lay-up tool comprising an upper tool surface, a plurality ofstiffener grooves formed into said upper tool surface; laying-up aplurality of resin impregnated stiffener fibers within said plurality ofstiffener grooves to form a plurality of stiffeners, said plurality ofresin impregnated skin fibers laid-up such that they are not alignedwith said plurality of resin impregnated stiffener fibers; laying up aplurality of resin impregnated skin fibers onto said upper tool surfaceand over said plurality of resin impregnated stiffener fibers to form animpact compliant outer skin, said impact compliant outer skin comprisingan outer skin surface, an inner stringerless skin surface, and a skinthickness; curing said plurality of resin impregnated skin fibers tosaid plurality of resin impregnated stiffener fibers such that saidplurality of stiffeners become integrated into said inner stringerlessskin surface.
 19. A method as described in claim 18, wherein: saidimpact compliant outer skin comprises 0/45/90 degree layup at 20/80/0percent ratios; each of said plurality of stiffeners comprises +/−60degree layup; and said plurality of stiffeners comprises hat framesincluding at least one cap element positioned therein comprising a 0degree layup interweaved with said resin impregnated stiffener fibers.20. A method as described in claim 18, wherein said upper tool surfacecomprises a plurality of multi-curved shapes.
 21. A method as describedin claim 18, further comprising: co-curing said plurality of resinimpregnated stiffener fibers and said plurality of resin impregnatedskin fibers to cure said plurality of stiffeners onto said innerstringerless skin surface.
 22. A method as described in claim 18,further comprising: co-bonding said plurality of resin impregnated skinfibers to said plurality of resin impregnated stiffener fibers to bondsaid plurality of stiffeners onto said inner stringerless skin surface.23. A method as described in claim 18, further comprising: filling a hatframe interior with foam prior to laying up said plurality of resinimpregnated skin fibers onto said plurality of resin impregnatedstiffener fibers, said foam tailored to meet varying impactrequirements.
 24. A method as described in claim 18, further comprising:varying the lay-up angles of said plurality of resin impregnated skinfibers to generate said impact compliant outer skin.
 25. A method asdescribed in claim 18, wherein said plurality of stiffeners comprises aplurality of circumferentially orientated frames including at least onecap element positioned therein, said cap element comprising S-2 glassplies.